Tab strip fin for heat exchanger cores



Oct. 20, 1953 v R, LYERLY ETAL 2,656,160

' TAB STRIP FINFOR `HEAT EXCHANGER coREs Filed June 4, 1951 f Y v TTR/VEY Patented Oct. 2G, 1953 2,656,166 TAB STRIP FIN Foa HEAT EXCHANGER coREs Ray L. Lyerly and Sven Holm, Wellsville, N. Y., assignors to The Air Preheater Corporation,

New York, N. Y.

Application June 4, 1951, Serial No. 229,805

6 Claims. (Cl. 257-245) The present invention relates to apparatus for the exchange of heat between two confined fluids and particularly to an improved form of extended fin surface for heat exchangers of the plate type.

A familiar type of heat exchanger for two confined fluids comprises metallic plates spaced apart to form fluid passages through which one fluid is circulated for transferring heat through the passage wall formed by the metallic plate to another fluid in an adjacent passage, the passages for the heating fluid and fluid to be heated being arranged in alternation. The spaces between the adjacent plates are closed along one pair of opposite edges to close the side of the fluid passages.

To increase the efciency of heat transfer between the two fluids through the passage walls the latter are frequently provided with extended surface in the form of fins that project into the fluid streams. The present invention contemplates improvements in extended surface in the nature of preformed elements that are mounted between and bonded to parallel plates to constitute extended surface of the passage Walls formed by the plates. Specifically the invention is directed to an improved form of s'o-called interrupted strip lin .that lies in the fluid passage\ and extends in the direction of fluid flow.

In designing heat exchangers generally and particularly heat exchangers for gas turbine application, it is desirable to arrange the unit for counterflow. Especially if higher effectivenesses are required, say 80% and higher, the counterflow principle is the only practical flow arrangement. The only disadvantage is that the designer does not have the freedom to select the optimum ratio of frontal areas for the two fluids as this ratio is established in counterilow and the frontal area is common for both uids.

In a gas turbine application, the heat is exchanged between gas at approximately atmospheric pressure and air at a pressure 4 or 5 times atmospheric pressure. The extended heating surface on gas side should be some very eliicient surface as pin-fins extending between widely spaced plates forming passages. The extended heating surface on the air side has heretofore been a channel shaped element or plates with corrugations, generally square, forming continuous strip fins extending between closely spaced plates that form the air passages.

It is the object of this invention to provide an extended surface element to replace the continuous I'ln surface heretofore used on the air side. The surface contemplated will have a higher kheat transfer rate and this improvement in heat transfer is even more pronounced at low or part .loads since the lm coefficient decreases with the .8 power with the mass velocity for continuous passages and approximately with the .65 power for interrupted passages.

The invention will best be understood upon reference to the following description of illustrative embodiments thereof when read in conjunction with the accompanying drawings in which:

Figure 1 is a transverse sectional View through part of a heat exchanger having passage walls provided with extended surface in accordance with the present invention.

Figure 2 is a fragmentary perspective view on an enlarged scale of one of the n elements illustrated in Fig. I.

Figure 3 is a plan View ofa metallic blank or strip from which the fin element of Fig. 2 is formed.

Figure 4 is a sectional View longitudinally of the heat exchange passages on the line ll-Il in Figure 1.

Figures 5 and 6 are sectional views similar to Figure 1 illustrating modified forms of the fin element.

In Figure 1 the numerals I0 and lI designate a pair of metallic plates spaced apart to form a passage I2 through which air or other fluid to be heated is circulated in heat transfer relationship with another iiuid such as hot gas flowing through passages I3 that alternate with the air passages I2 and which are separated therefrom by passage walls constituted by the plates I2 and I I. The extended fin surface projecting from the walls Il) and II into the air passage I2 is, in accordance with the present invention, made up of a plurality of fin elements, designated as a whole by the numeral It, disposed in side by side relation in the passage Il and preferably bonded to the confronting surfaces of the plate walls IIJ and II that bound the passage.

Each of the iin elements I4 is formed from an elongated strip of metal I5 which is slit at I6 as indicated in Fig. 3 part-way in from each longitudinal side edge I'I so that tabs may be bent upwardly and downwardly, as shown in Figure 2, fromvthe web or body portion It of the strip. The tabs 20 are bent upwardly along opposite longitudinal edges of the body or web I8 vof the strip in alternation with other tabs ZI which are bent downwardly from the body portion. The extreme marginal edges of all the tabs are also bent to parallelism with the web I 8 so as to provide lateral flanges 22 at right angles to the tabs 20. These -flanges 22 constia tute foot-like portions which rest against the surfaces of the plates I and I I.

In constructing a heat exchange envelope a plurality of the iin elements Id shown in Fig. 2 are assembled in side by side relation between the two plates t0 .and Il which constitute the walls ofV a heat exchange envelope. The ele'- ments i4 are mounted on the plate Il so that the side faces 23 of the lateral flanges 22 on adjacent elements Ill are in contact with each other as appears in Fig. l. The plate I'lis then laid on the juxtapositioned elements I4 and the ele-v ments at the extreme side edges. of the plates lll and Il may be tack welded. thereto prior' to brazing all of the fin elements to the plates l0, H, strips of brazing metal etc. having been laid between the element feet 22 and 'the'pla'tes F0", I1 in the course of assembly.

The relative proportions of the web I8 of the fin elementl lill and thetabs 2G, 2l .are such that the hydraulic diameter of either oi. the spaces a, Fig. 1.betweenV two tabs .2B or 2i on a particular element equals the hydraulic diameter of the space b formed between two adjacent elements id by the spacing apart of the latter throughthe foot-like lateral -flanges 22 o-f these elements.

On the gas side of the plate walls l0', l'l extended surface may be provided in the passages I3 by pin-hns 3d as more fully disclosed in the c'o-pending application of Sven Holm andy Arthur Jensen, Serial No. 752,008`,iiled June 3, 19217., now Patent #2,595,457 granted May 6, 1952. In' a heat exchanger made up of a plurality o'f envelopes of the type described, the side edges of the passages are closed by plate members 31 and, when the gases ilow in passages i3 in counterflow relation to the air in passages i2, the corresponding spaces `between adjacent envelopes are closed along the side edges of the latter by other bridging elements `or strips 32 in conventional fashion.

In Fig. the web portion S3 of each fin' element is formed with alternately raised and depressed portions 35 and 35 so that the surface of the web is interrupted and non-planar in the direction of gas now so Ias to avoid formation of a laminar boundary layer along the 'longitudinal surface of the web 33'.

The-iin element 313 shown in Fig. 6'v is similar to that of Fig. l except that the tabs are bent more to a- VeshapeV thanv to the U or channel shape shown in Fig. l.

'The fin elements i6 as vdescribed permit amore balancedV heat exchange design when used with other 1highly efficient surfaces Aon the other side of dividing wall, resulting in a shortr iiow path in the heat exchanger. The-elements' 'I4 are selfspac-ing and the envelope may be lled with the elements Aand the outside-ones can be -taclr welded to plates before braz'ing. 'There 'isY 1a `minimum of doubling up of material. A conventional surrace built up of channel components or corrugated sheets has 50% of doubled up surface, i'. e. half the wall surface or section is contacted and vover-laid 'by .a corresponding' part of a -so .that there is adouble thickness of metal in these regions amounting in all to about half the ywall surface. The 'surface' here described has only Abetween 16 and 1.7% doubled up Vsur-tace.

A further advantage is 'that an interrupted 4strip fin may be produced without the usual large loss of material vin cutting away parts of. continuous longitudinal fins to create the interrupted form. Here the'fonlylossxoi material. is .thefvery What we claim is:

l. In a heat exchanger having metallic plates spaced apart as walls of iiuid passage; a plurality of longitudinal n elements mounted in said passage in side by side relation each comprising an. elongated` metallic strip disposed in spaced relation to' said walls and formed with pairs of marginal tabs extending from each longitudinal edge alternately in opposite directions from the plane of the body of the strip toward the opposite walls' of said passage to provide alternately upright and inverted generally U-shaped channel parts withend portinns of the tabs contacting saidrwalls.

2. In.-a..heat exchanger having metallic plates spaced apart as walls of a fluid passage; a plurality of longitudinal fin elements mounted in said passage in side by side relation each comprising an elongated metallic ystrip disposed in spaced relation to said walls .and formed with pairs of marginal tabs extending from each longitudinal edge-alternately in opposite directions from the plane of `the-body ofthe strip toward the opposite walls of said` passage to provide alternately upright and inverted generally U-shaped channel parts; 'and lateral flanges at the extreme end portions of the tabs bent laterally at approximately a' right angle to each tab to provide foot-like portions in con-tact with the Walls of said fluid passage, the sidey faces of the flanges contacting corresponding 'parts of the .next contiguous nn elements at either side 'thereof to subdivide the space Vbetween said platesv .intov passage sections located between contiguous elements and adjacent to other passage sections enclosed within said U-shaped channel parts of each element.

3. Ina heat exchanger .having metallic plates spaced apart as Walls-of a` fluid passage; a plurality of longitudinal n elements mounted in said passage. in side by side .relation each comprising an elongated metallic stripY located centrally between said -Walls formed with pairs of marginal tabs extending from each longitudinal edge alternately in opposite kdirections from the plane of the body Iof the Vstrip toward the opposite walls of said passage to provide alternately upright and inverted generally 'U -shaped channel parts with end portions of the tabs contacting `said walls, the widthof the body portion of said element dividing the height of the nuid passage to form two complementary portions of the same frontal area and hydraulic diameter bounded laterally by the tabs extending normally from the body portion of the tabs.

4.. In a heat 4exchanger havingv metallic plates spaced apart as walls of a uid passage; a plurality of longitudinal n elements mounted in said passage in side by :side relation each comprising .an elongated metallic strip located centrally between said: Walls.; pairs of marginal tabs extending in/opposed relation Ain one direction from the plane of the body of each strip to provide generally `U-'shap'ed upright channel parts; other pairs of opposed vtabs extending in the opposite direction from the body of the strip to provide inverted generally U -shaped channel parts; lateral. flanges at' the extreme end portions of. theftabs bent laterally at approximately right vangles thereto lto provide foot-like portions in contact with the walls of said uid passage and the s'idefaces vof said ilanges contacting corresponding parts of Ithe next contiguous 1in elements at either side thereof rto sub-divide the .space between said plates into passagesections located betweencontiguous elements and adjacent to other passage sections enclosed within said U-shaped channel parts of each element, the width of the body portion of said element bisecting the height of the iluid passage to form two complementary portions of the same frontal area and hydraulic diameter bounded laterally by the tabs extending normally from the body portions of the strip and the width of the lateral flanges of contiguous members being such that when their anges abut the passage areas between the tab elements ofv contiguous fin elements have a frontal area and hydraulic diameter the same as embraced within a U-section of a n element.

5. In a heat exchanger having metallic plates spaced apart as walls of a fluid passage; a plurality of longitudinal fm elements mounted in said passage in side by side relation each comprising an elongated metallic strip located centrally between said walls formed with pairs of marginal tabs extending from each longitudinal edge alternately in opposite directions from the plane of the body of the strip to provide alternately upright and inverted generally U-shaped channel parts, the width of the body portion of said element subdividing the height of the fluid passage to form two complementary portions of the same frontal area and hydraulic diameter bounded laterally by the tabs extending normally from the body portion of the tabs and the 6 spacing of the U-sections of any two contiguous fin elements being such as to form therebetween another passage section of a frontal area corresponding to that embraced with a U-section of a fin element.

6. In a heat exchanger having a pair of metallic plates spaced apart as walls of a uid passage; longitudinally extending n elements constituting extended surface projecting from said walls into said passage comprising; elongated metallic strips having the body portions thereof disposed centrally between said plates and parallel thereto with side portions of the strips extending alternately in opposite directions substantially normally to its body toward both said wall plates of the passage and subdividing the latter.

RAY L. LYERLY.

SVEN HOLM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,311,637 Boblett July 29, 1919 2,378,646 Manning June 19, 1945 2,413,179 Grandmont et al. Dec. 24, 1946 2,419,234 Holhan Apr. 22, 1947 2,439,208 Gloyer Apr. 6, 1948 2,571,631 Trumpler Oct. 16, 1951 

